Electric furnaces are widely used for various metal smelting and refining operations. The typical furnace may include a plurality of carbon or graphite electrodes which extend through openings in the roof of the furnace to a location adjacent the level of the melt in the furnace. Typically, the furnace may include several 2-foot or greater diameter electrodes.
When molten material is tapped from the furnace, the level within the furnace lowers and it is necessary to lower the electrodes to follow the level of the melt in the furnace. Then, when additional charge is added to the furnace, the electrodes must be retracted to maintain them at the proper distance from the melt in the furnace. As the arc from the electrodes smelts or melts the furnace charge, the ends of the electrodes erode. Further, the massive electrodes are constantly lowered and lifted automatically by suitably controlled winches or other drive means to maintain proper operating conditions.
To avoid the escape of hot dust laden and frequently noxious gases with the corresponding environmental hazards and loss of heat and efficiency of the furnace, it is necessary to provide a good seal between each electrode and the furnace. Unless a reasonably gas tight seal is maintained, rapid erosion, and/or oxidation, including necking in of the electrode occurs along that length of the electrode which extends through the electrode opening in the furnace roof. Such erosion not only weakens the electrode, with the danger that the lower end of the electrode can break off, but also reduces the diameter of the electrode with the result that the current carrying capacity of the electrode is substantially reduced. In addition, the size of any opening between the electrode and the furnace increases as the electrode erodes which allows even more gas to escape. Tests show that typical temperatures of gases when flowing outwardly from a furnace through the annulus between the furnace opening and the electrode are on the order of 3,000.degree. F., and hence, the electrode as well as surrounding structures and equipment can be damaged by the escaping hot gases.
Because of the large current carried by each electrode, the heat of the furnace and the vibration caused by the arc between the end of the electrode and the furnace melt, it is virtually impossible to provide a reliable close fitting seal without danger of damage to the electrode or the roof of the furnace through which the electrode extends. In addition, as a result of conditions within the furnace, the axis of the electrode may tilt slightly which presents further problems with a close fit of the electrode in the furnace opening. Further, there is no known seal material which can withstand the high temperatures at the electrode surface.
As previously explained, the electrodes are frequently lifted and lowered during operation of the furnace. When the electrode is lowered, it is also subjected to slag splashing from the furnace. If a close fitting opening or seal is provided at the furnace, slag on the outer surface of the electrode can damage the seal when the electrode is elevated.
While in many instances the pressure within the furnace is greater than atmospheric, there are times when below atmospheric pressure exists in the furnace. Such conditions may arise where especially noxious gases are emitted by operation of the furnace and such gases must be removed from the furnace by vacuum to avoid operator or worker hazards.
It is also desirable to maintain the region of the outside of the furnace near the electrode as cool as possible to avoid damage to electrode control and manipulating equipment, as well as to reduce hazards to the workers.
Consequently, there is a need for a reliable arc furnace electrode seal which seals under conditions of both positive and negative pressures in the furnace, which in no way interferes with adjustment or manipulation of the electrode, and which requires minimal maintenance. In accordance with this invention, such an electrode seal is provided.